Science has the potential to do much good. But it can also be misused and cause harm. How can researchers become aware of the risks and share their insights responsibly? This volume gathers a premier group of scholars and practitioners to address cutting-edge dilemmas of "responsible policy engagement." The authors reflect on their own experiences and provide guidance on how to constructively communicate with policymakers - while also being transparent about the uncertainty and subtleties of the research process. The case studies cover tricky policy engagements on topics ranging from postconflict power-sharing, atrocities prevention, NATO enlargement, economic crises, and business and human rights to counterinsurgency and state-building, census data and polling, and intelligence analysis. To avoid pitfalls, the analyses offer a mix of ethical principles and practical advice, including setting cautionary ethical redlines, reflecting on one's position and values, and describing areas of consensus and degrees of uncertainty. Speaking Science to Power uncovers the temptations scholars may face to share particular results, overgeneralize findings, conceal uncertainty, or curry favor with policymakers, and then urges them to act responsibly.